German Chancellor Angela Merkel speaks at the headquarters of SPD for preliminary coalition talks on January 7, 2017.

Germany's Christian Democrats (CDU) meet on Monday to approve a coalition deal with the Social Democrats (SPD), a move that will take their leader, Angela Merkel, a step closer to a fourth term as chancellor in Europe's biggest economy.

The last major hurdle to end a five-month political impasse after a September 24 election, however, comes next week. On March 4, the results of a postal vote by SPD members vote will be announced, and that result is far less certain.

The party conference follows Merkel's announcement of her CDU picks for a new, younger cabinet intended to revive the party, which has descended into rows about how to respond to the far-right Alternative for Germany (AfD).

Merkel is to address CDU delegates at the meeting before the vote on the deal, which is expected to go through easily.

The conference will also vote on the appointment of her close ally Annegret Kramp-Karrenbauer as CDU general secretary, who is widely seen as her preferred successor. Dubbed "mini-Merkel" by some media, the Saarland state premier, 55, shares many of Merkel's views - but not all.

Her Catholic, western German background contrasts with Merkel's Protestant, eastern roots. While socially conservative, known for opposing gay marriage, Kramp-Karrenbauer is a strong supporter of the minimum wage and worker rights.

After 12 years as chancellor and almost 18 years in charge of her party, Merkel's authority is waning and on Sunday, she responded to growing calls for new blood at the top of the CDU.

In a bid to silence critics who want the CDU to shift to the right to win back voters from the AfD, Merkel said she would promote her most outspoken critic, 37-year-old Jens Spahn, to the cabinet.

She said she had carefully chosen a younger team who could bring energy to the job and revive the party's mood.

After her conservative bloc, which also includes Bavaria's Christian Social Union (CSU), scored its worst result since 1949 in last year's election, her efforts to forge a coalition with two other smaller parties collapsed in November.

This forced her to woo the SPD, a reluctant partner, which had seen its own support fall to its lowest since World War Two.

If SPD members vote "no" in their ballot, the most likely outcome is a new election or possibly a minority government.

Some analysts say the prospect of a new election will spur SPD members into voting "yes", to prevent further deterioration in the party's support. An Emnid poll on Sunday showed the SPD down two points from a week ago, at 17 percent. (Reporting by Madeline Chambers, editing by Larry King)